const BALLS_COUNT = 25;
const BALL_SIZE_MIN = 10;
const BALL_SIZE_MAX = 20;
const BALL_SPEED_MAX = 7;

// 设定画布和初始数据
const para = document.querySelector('p');
const canvas = document.querySelector('canvas');
const ctx = canvas.getContext('2d');

// 将画布窗尺寸置为窗口内尺寸
const width = canvas.width = window.innerWidth;
const height = canvas.height = window.innerHeight;

// 设定形状类层次结构
class Shape {
  constructor(x, y, velX, velY, exists) {
    this.x = x;
    this.y = y;
    this.velX = velX;
    this.velY = velY;
    this.exists = exists;
  }
}

class Ball extends Shape {
  constructor(x, y, velX, velY, color, size, exists) {
    super(x, y, velX, velY, exists);

    this.color = color;
    this.size = size;
  }

  draw() {
    ctx.beginPath();
    ctx.fillStyle = this.color;
    ctx.arc(this.x, this.y, this.size, 0, 2 * Math.PI);
    ctx.fill();
  }

  update() {
    if ((this.x + this.size) >= width) {
      this.velX = -(this.velX);
    }

    if ((this.x - this.size) <= 0) {
      this.velX = -(this.velX);
    }

    if ((this.y + this.size) >= height) {
      this.velY = -(this.velY);
    }

    if ((this.y - this.size) <= 0) {
      this.velY = -(this.velY);
    }

    this.x += this.velX;
    this.y += this.velY;
  }

  collisionDetect() {
    for (let j = 0; j < balls.length; j++) {
      if ( this !== balls[j] ) {
        const dx = this.x - balls[j].x;
        const dy = this.y - balls[j].y;
        const distance = Math.sqrt(dx * dx + dy * dy);

        if (distance < this.size + balls[j].size && balls[j].exists) {
          balls[j].color = this.color = randomColor();
        }
      }
    }
  }
}

class EvilCircle extends Shape {
  constructor(x, y, exists) {
    super(x, y, exists);

    this.velX = BALL_SPEED_MAX;
    this.velY = BALL_SPEED_MAX;
    this.color = "white";
    this.size = 10;
    this.setControls();
  }

  draw() {
    ctx.beginPath();
    ctx.strokeStyle = this.color;
    ctx.lineWidth = 3;
    ctx.arc(this.x, this.y, this.size, 0, 2 * Math.PI);
    ctx.stroke();
  }

  checkBounds() {
    if ((this.x + this.size) >= width) {
      this.x -= this.size;
    }

    if ((this.x - this.size) <= 0) {
      this.x += this.size;
    }

    if ((this.y + this.size) >= height) {
      this.y -= this.size;
    }

    if ((this.y - this.size) <= 0) {
      this.y += this.size;
    }
  }

  setControls() {
    window.onkeydown = e => {
      switch(e.key) {
      case 'a':
      case 'A':
      case 'ArrowLeft':
        this.x -= this.velX;
        break;
      case 'd':
      case 'D':
      case 'ArrowRight':
        this.x += this.velX;
        break;
      case 'w':
      case 'W':
      case 'ArrowUp':
        this.y -= this.velY;
        break;
      case 's':
      case 'S':
      case 'ArrowDown':
        this.y += this.velY;
        break;
      }
    };
  }

  collisionDetect() {
    for (let j = 0; j < balls.length; j++) {
      if (balls[j].exists) {
        const dx = this.x - balls[j].x;
        const dy = this.y - balls[j].y;
        const distance = Math.sqrt(dx * dx + dy * dy);

        if (distance < this.size + balls[j].size) {
          balls[j].exists = false;
          count--;
          para.textContent = '还剩 ' + count + ' 个球';
        }
      }
    }
  }
}

// 球和恶魔圈
const balls = [];
const evilBall = new EvilCircle(
  random(0, width),
  random(0, height),
  true
);
let count = 0;

// 执行动画
loop();

// 生成随机数的函数
function random(min, max) {
  return Math.floor(Math.random()*(max-min)) + min;
}

// 生成随机颜色的函数
function randomColor() {
  return 'rgb(' +
         random(0, 255) + ', ' +
         random(0, 255) + ', ' +
         random(0, 255) + ')';
}

// 定义一个循环来不停地播放
function loop() {
  ctx.fillStyle = 'rgba(0, 0, 0, 0.25)';
  ctx.fillRect(0, 0, width, height);

  while (balls.length < BALLS_COUNT) {
    const size = random(BALL_SIZE_MIN, BALL_SIZE_MAX);
    const ball = new Ball(
      // 为避免绘制错误，球至少离画布边缘球本身一倍宽度的距离
      random(0 + size, width - size),
      random(0 + size, height - size),
      random(-BALL_SPEED_MAX, BALL_SPEED_MAX),
      random(-BALL_SPEED_MAX, BALL_SPEED_MAX),
      randomColor(),
      size,
      true
    );
    balls.push(ball);
    count++;
    para.textContent = '还剩 ' + count + ' 个球';
  }

  for (let i = 0; i < balls.length; i++) {
    if (balls[i].exists) {
      balls[i].draw();
      balls[i].update();
      balls[i].collisionDetect();
    }
  }

  evilBall.draw();
  evilBall.checkBounds();
  evilBall.collisionDetect();

  requestAnimationFrame(loop);
}
